Coating process and apparatus



W. 0. SNELLING.

COATING PROCESS AND APPARATUS APPLICATION man MAY 3|. 1916.

INVENTOR Aww Patented J luly 15, 1919.

PATENT OFFICE.

WALTER 0. SNELLING, F LONG ISLAND CITY, NEW YORK.

COATING PROCESS AN'D APPARATUS.

. Queens and State of New York, have invented a new and useful Improvement .in

Coating Processes and Apparatus, of which v the fol Wing is a specification'.

My invention relates to coating processes and apparatus, and has special reference to the production of imperforatev coatings upon fragmentary material of a hygroscopic nature such, for example, as crystalline ammonium nitrate.

The general object of my invention is to provide a simple, effective and readilyl controllable process of producing uniform surface coatings upon granular material, together with suitable apparatus for carrying such process into effect.

Another and more specific object of my invention is to provide a process of indi; vidually coating ammonium nitrate crystals, and other liygroscopi'c substances, with Waterproof coating materials such as nitronaphthalene. This application of my invention is of ,special utility in the manufacture of certainexplosives which may contain both ammonium nitrate and nitronaphthalene as active ingredients.

In the accompanying drawing, Figure 1 is a side view, partly in vertical section and partly in elevation, showing somewhat diagrammatically one form of apparatus suitable for use in practising my invention, and Fig. 2 isf a horizontal sectlonal view of a portion of the structure of Fig. 1, the section being taken substantially along the line II-II, Fig. 1. T

My invention consists broadly in applying' coating materials in the form of condensable vapors instead of in liquid or semiliquid formas is usual. Therefore, while I shall describe my process with specific-referenceto the coating of ammonium nitrate crystals with nitronaphthalene, it is to be understood that. my invention l:is lby no means limited to the use of these'particular substances., The general procedure which I employ consists in vaporizing the coating material and bringing the resulting vapor into contact with the'objects to bey coated,

which should preferably be cold enough to Specication of Letters Patent. V

Patented July 15, 1919.

Application le May 31, 1916. Serial No. 100,846.

.condense sufficiently thick layers of the coatmg medium upon their surfaces during a relatively brief treatmentwith the Vapor. When masses of crystals or other granular or fragmentary materia/ls are treated, I prefer to deposit the granular material in a treating chamber filled with the coating vapor, 1n such a way as to cause the grains to fall freely one or more times through the vapor, thus taking on individual and uniform coatings, thetthickness of which de pends upon the temperatures of the materials, the density of the vapor and the time of treatment, factors which may be readily controlled in accordance with the circumstances of each particular case.A

Ammonium nitrate is a desirable ingredient in certain forms of explosives, but on account of its very hygroscopic nature it must be .thoroughly protected from i-moisture When the explosive is also to contain nitronaphthalene, it is customary Vto mix the am. 75 monium nitrate with the nitronaphthalene,- for the purpose of excluding moist air from the hygroscopic salt, by melting the nitronaphthalene and stirring the ammonium nitrate into the liquid mass until the grains of r ammonium nitrate are covered with the ni-` tronaphthalene. Under these conditions,

, many ofthe individual ammonium nitrate grains are not completely coated unless a very large proportion of nitronaphthalene is employed, and the use of such large amounts of nitronaphthalene is often undesirable.

By means of my present process, I am able to cover ammonium nitrate crystals with thin coatings of nitronaphthalene, using only a small percentage of the coating material. r For this purpose, I may make use of the apparatus shown in the accompanying drawing, such apparatus comprising a c1rculartower or chamber 1, a recep- 95 tacleQ for the granular material to be Vtreated, a second receptacle 3 for the coated product, and screw conveyers 4 and 5, inclosed in tubular casings 6 and 7, respectively, for transferring material from the i receptacle 2 to the upper end of the tower 1 and for removing the coated grains from the bottom of the tower 1 to the receptacle 3.

The material delivered by the conveyer 4 should be caused to drop through the tower 105 1 ina regular and Well scattered shower.

-and l1 are preferably unequal in number,

in order that son'ie of the slots may register to a greater or less extent at all times, thus '-livered-byt'he conveyor 4 shallbe producing regular delivery of the-granularmaterial. lhe rotating plate 11 is provided with a peripheral flange 15," which moves beneath an annular flange 16 secured to the inner wall of thetower 1,--thisrrarf-- rangement insuring that-'the material ldedeposited upon the platev 11.

Vapors of nitronaphthalene or other suitable coating material are introduced into theV tower 1l through a-pipe 20, controlled by a valve21 and communlcating-wlth a vaporlzing vessel or still 22 which is provided with l a suitable heater 23 and which may contain commercial nitronaphthalene, consisting chiefly of a-mono-nitronaphthalene and boiling at about304 C. This material begins to decompose at approximately its Jooiling y point, and for this reason, the system including the tower 1. the receptacles 2 and 3, the

c'onveyer tubes and 7, and the vaporizer 22 is preferably maintained under subatmospherie pressure, the pressure being reduced sufiiciently to lower the boilingpoint of the nitronaphthalene Well below its decomposing temperature. In the system shown herein, the necessary reduced pressure is maintained by means of a. suction pump 25 whic-h conimunicates with the interior of the tower 1 through a pipe 26T The supply of nitronaphthalcne vapors should be so regulated with respect to the amount oi ammonium nitrate being treated, that as much of the vapor as possible is condensed upon the crystals. However, some of the vapor will necessarily be withdrawn through the exhaust pipe and in order to recover this vapor, I interpose in the pipe 26 a condensing worm 27 inclosed in a casing 28 in which a cooling fluid may be circulated through inlet and outlet pipes 29 and 30. This circulating fluid must not be so cold as to solidify the nitronaphthalene in the condensing Worm, and I therefore prefer to en'lploy hot water for this purpose. The liquid nitronaphthalene condensed in the worm 27 flows into the vaporiZer 22 through a short drain pipe 31 attached to the lower bend of the exhaust pipe 2G;- y

l The feeding receptacle 2 is preferably provided with a tightly fitting cover 32 and the discharge receptacle 3 is also provided with properly' shown, this valve consists of a plate 34 slidably supported just above the inlet of the receptacle 3 and controlled by means ofa handle 35.- The discharge receptacle may also beprovidcd witha valve 36 for admitting air to the receptacle when it is desired. to open the door i i In the operation of the 8bove-described apparatus to treat ammonium `nitrate nystals with nltronaphthalenef the: Veo'ld--fam-'-1- monium-nitrate, in as dryaz condition as possible, -i's placed in the receptacle 2, heat is applied to the vaporizer 22, and the suction pump 25, the screw conveyers 4 and and the driving shaft 14.- of the distributer plate 11`are all set in motion. The nitrate crystals are fed into the tower 1'l inan evenly-distributed shower, and as they fall, they condense -the nitromiphthalene vapor invthin layers upon their. surfaces. The coated grains are then conveyed to the, discharge receptacle 3, either directly and without further treatmentv or through an air blast or Jother suitable chilling means, if such chilling is found to be necessary in order to complete the solidification. of the nitronaphthalene coatings. It may be found desirable to chill the ammonium nitrate crystals before introducing them into the treating chamber, in order that coatings of greater thickness may be formed.- It may also be found desirable to dilute the vapor within the treating chamber with nitrogen, or sonne other inert gas, if particularly thin coatings are desired.

The treating chamber 1, instead of being a stationary tower, as shown, may take the form of a rotatingr drum, of the form'well known in tumbling land drying apparatus, the granular material and the coating vapor being introduced axially into the drum and the grains being .turned over repeatedly in their passage through the drum, which may be 'inclined toward its .discharge end and may be provided with suitable stirring baffles in a well known manner.

As I.. have indicated above my invention is not confined to thecoating of ammonium nitrate crystals or to the use of nitronaphthalene as the coating material; nor'are the specific forms of apparatus which I have shown and described the only forms which may be employed within the limits of my invention. Sodium nitrate, as a further example, may be prepared for the manufacture of dynamite or Iblack blasting powder by applying coatings of naphthalene, nitronaphthalene or the like, according to the foregoing process, and grains of ordinary V30 5. The

black'powder may be similarly coated with protective materials, suitable precautions be- 4 ingtaken, by reducing the pressure on the vapor or' otherwise, to insurey that the tem- 5 perature of the vapor is well below the ignition point of the powder. It will thus be evident that numerous v-ariations both in materials, apparatus and process steps may readily be devised 'by persons skilled in the 3. The process that comprlses artiically..

cooling a solid substance and treating the cooled substance with a vaporous coating material. y

4. The process that comprises artificially cooling a fragmentary hygroscopic substance and treating the cooled substance with a vaporous coating material.

rocess that comprises causing a hygroscoplc fragmentary substance to all l freely through a vaporous condensable coating material.

6. The rocess thatcomprises causing al.

A hygroscoplc fragmentary substance to freely through a vaporous coating/material the solidifying temperature of which is higher than the temperature of the said substance. l

7. The process that comprises treating a -hygroscopic substance with a vaporous coating material under subatmospheric pressure.

8. The rocess that comprises treating a i hygroscopic crystalline substance with a Vaporous coating material under sub-atmospheric pressure.l

9. The process that comprises treating a lfragmentary hygroscopic substance; with a 50, vaporous coating material diluted with an inert gas.v

10. The process that comprises treating a hygroscopic substance with nitronaphthalene vapor.

11. The process that comprises treating a hygroscopic substance with nitronaphthalene vapor under subatmospheric pressure.

12. The process that comprises causing a hygroscopic substance to fall freely through nitronaphthalene vapor.

'13. The process that com rises treatin a hygroscopic substance wit nitronapht alene vapor maintained at a temperature below the decomposing temperature of nitronaphthalene.

. porizing means un 14. The process that comprises` treating' crystalline ammonium nitrate with a vaporous coating material. l w v 15. The process that comprises causing crystalline ammonium nitratcto fall ,freely throu h a vaporous coating material. 16. he process that comprises treating crystalline ammonium nitrate with nitronaphthalene vapor.

17. The process thatl comprises causing 75 crystalline ammonium nitrate to fall freely through nitronaphthalene vapor.

18. The process that comprises` treating crystalline ammonium nitrate with nitronaphthalene vapor under,y subatmospheric pressure. J

19. The process vthat comprises vaporizing a normally solid coating material that decomposes at approximately its normal boilin oint, under subatmospheric -essure su' ciently low to substantially re uce the saidboiling point, and bringing the resulting vapor into contact with the material to -be coated.

20. The process that comprises nVaporizing nitrona hthalene under subatmospheric pressure su ciently lowto substantially pre- Vent decomposition of thenitronaphthalene, and bringing the resulting vapor into con tact with crystalline ammonium nitrate. y

21. Apparatus for coating fragmentary material comprising a treating4 vessel, means for causing the material to be coated to fall therein, means for vaporizing a coating material and for introducing the resulting vapor into the said Vessel, and means for maintaining both the material being vapor- .ized and-the said vessel under subatmospheric pressure.

` 22. Apparatus for coating fragmentary material comprising a treating Vessel, a feeding hopper communicating with the top of the said vessel, a receiving receptacle'` communicating with the bottom of the said vessel, means for conveyino' fragmentary material from the said fee ing hopper to the said treating, Vessel and from the said treating vessel to the said receptacle, means for vaporizing a coating material and for introducing the resulting vapor into the said vessel, and means for maintaining the said treating vessel, ho per, receptacle and vader subatmospheric 'pressure. v

23. Apparatus for coating fragmentary material comprising a treating vessel, a hopper, a conveyer for bringing fragmentary material from the said hopper to the top of the said treating vessel, and a feeding device disposed at the top ofthe said treating vessel and comprising two superposed and perforated disks, the said disks being relatively movable to progressively bring the perforau tions in the said disks into almement.

24. Apparatus for coating fragmentary 13o nmterial comprising a treating vessel, a hoprelatively movable to progressively bring per. :1 conveyer for bringing fragmentary the slots in the saidvdisks into alinement. material from the suid'hoppei' to the top of In testimony whereof, I have hereunto 10 the said treatingvessel, :und e feeding device subscribed niy name this 25th day of May, disposed :it the top of the sind treating ves- 191'6.

sul und conlprieing two supel'posed and radially Slotted disks, uw Suid disks being WALTER o. SNELLING. 

